CN117620112A - Pressing method for square (or rectangular) billet continuous casting - Google Patents

Abstract

The invention relates to a method for pressing square (rectangular) billets, which is characterized in that a transverse low-power sample is taken from an unrepressed billet, and a drilling and chip removing method is adopted to obtain a pressing key position; the first withdrawal and straightening machine after the critical position is pressed down by adopting a single-roller rule, and the withdrawal and straightening machine before the critical position is pressed down by adopting a multi-roller rule. The quantitative method for determining the control pressing parameters changes the defect of pressing at a manually specified multi-section or fixed position, overcomes the problems of small section, short solid-liquid two-phase area and difficult catching of pressing positions of square (or rectangular) billet continuous casting machines, and has better application effect than the traditional light pressing and heavy pressing processes.

Description

Pressing method for square (or rectangular) billet continuous casting

Technical Field

The invention belongs to the technical field of metallurgy, and relates to a method for pressing square (or rectangular) billet continuous casting.

Background

With the deep development of continuous casting technology in the steel industry, the production of high-quality defect-free casting blanks becomes an important target for many metallurgical workers. For continuous casting billets, center segregation and porosity and shrinkage cavity are problems which are always concerned and are urgently needed to be solved. The soft reduction technology compensates the solidification shrinkage of the central liquid core through the pressure acted on the surface of the casting blank, and the center segregation defect of the casting blank is extremely effectively reduced.

In the 70 s of the 20 th century, the japan NKK company proposed the concept of continuous casting billet reduction, and a good effect was achieved by adopting closely packed small segment type nip rolls, which marked the formal birth of a light reduction process. 80. In the early years, the Japanese new day iron test shows that the soft reduction technology not only can improve the defects of shrinkage cavity, looseness and the like, but also has good improvement effect on center segregation. Along with the gradual maturation of the reduction process and the development of an automatic technology, the online remote dynamic control of a continuous casting slab roll gap SMART sector section is successfully realized by an Olympic Union (VAI) in a RAUTARUUUKKI steel mill of Finland in the middle 90 s, and the formal birth of a dynamic soft reduction technology is marked. In 2010, a slab online solidification end heavy pressing technology is developed firstly by new japanese iron and gold, and then, a bloom solidification end heavy pressing technology is developed jointly by new japanese iron and gold and Japanese Aiduo steel, and experiments show that the heavy pressing technology obviously improves the defects of central shrinkage cavity and looseness, and the heavy pressing technology starts to be focused by the industry. The continuous casting technology in China is early in development, but is basically behind the western countries in 80-90 s, the continuous casting process is behind, and the continuous casting ratio is very low. At the later stage of 90 s, various domestic large steel enterprises introduce dynamic soft reduction processes, and the continuous casting soft reduction processes in China are gradually improved to the world advanced level. The domestic heavy pressing process is almost synchronous with the foreign development, for example, the heavy pressing process of medium plates represented by Bao steel and Tang Gang and the heavy pressing process of billets represented by Pan steel and Date are in the leading position in the world industry. Key technologies are also mastered step by design courts and universities in related fields in China, and the design courts and universities have independent intellectual property rights.

From the search of the patent, the northeast university, the middle yohike city, the middle yohike died, the Beijing university of science and technology, the western institute of weight, radium and the Chongqing university all have patent layouts, for example, each of the patent CN104057049A and the CN105689664A provides a device for single-roll heavy reduction of a sector section, the patent CN1772415A provides a reduction device for a solidification end rolling mill structure, the patent CN103878331A provides a sector section device for composite heavy reduction, the patent CN103949602A provides a sector section device capable of independently adjusting the reduction of a heavy reduction roller, the CN102189102B provides a single-roll heavy reduction process in terms of heavy reduction process, the patent CN106735026A provides a process combining single-point heavy reduction of a plurality of sector sections with continuous heavy reduction of sector sections, the patent CN106001476A provides a method for continuous dynamic heavy reduction of two stages, the patent 104874758A provides a control method for heavy reduction positions, and the patent CN110871265A provides a method for large square billet and a plurality of rolls Shan Tu. While the heavy pressing apparatus aspects referred to in the above patents are focused on the design and manufacture of roll trains or segments that ensure heavy pressing, most of the heavy pressing processes referred to are either increasing the total pressing on a soft pressing basis or increasing the pressing of one or more rolls or segments, or using a single raised roll to achieve heavy pressing, which is substantially similar to the soft pressing process.

A large number of factory tests show that the light pressing of the square billets is carried out at a position within the range of 0.2-1.0 of the central solid phase fraction, and generally, the single-roller pressing amount is not more than 5mm, the total pressing amount is not more than 20mm, and the total pressing rate is not more than 4mm/m. The heavy pressing method is to increase the total pressing amount based on light pressing, to increase the single pressing amount of one or several pressing rollers in the position with high solid phase fraction, or to use special pressing rollers, such as convex pressing rollers. The development history and engineering application of the carefully carded under-stress process will find that these under-stress processes are essentially focused on medium or extra thick slab or bloom casters, such as, for example, the large t 370 x 490mm, the climbing steel 360 x 450mm, the shao steel 320 x 425mm, etc. These models share the commonality: 1) The blank is large, the solidification rate is small, and a long two-phase region exists; 2) The number of the two-phase zone tension leveler is more, usually 6 to 8 frames are needed, the pressing position is convenient for capturing, and the equipment is easy to realize; 3) The distance between the frames is loose, so that hydraulic and three-electric systems can be conveniently arranged, and the control is easy to realize; 4) The section is larger, so that the convex roller type heavy pressure can be easily realized.

From the use effect, the improvement of the center porosity defect by the heavy pressing process is obviously superior to the improvement of the center shrinkage cavity by the traditional light pressing process, and the improvement of the center segregation is not the same as the improvement of the center shrinkage cavity by the traditional light pressing process. The practice of most enterprises is that the method has no obvious advantage over the traditional soft-reduction process, and the practice of a small part of enterprises is not the same as the traditional soft-reduction process. In addition, these existing heavy-press methods have limitations, and cannot be generalized to small square (or rectangular) billet continuous casting machines at present, mainly for the following reasons: 1) The square (or rectangular) billet continuous casting machine (especially the section below 200X 200 mm) has a smaller billet shape, and the solid-liquid two-phase area is much shorter than that of the above large square billet under the casting condition of the same steel grade; 2) The number of the two-phase area frames is small, usually not more than 5 frames are needed, the pressed position is difficult to capture, and the equipment is difficult to realize; 3) The distance between frames is very small, and great design barriers exist in the construction of hydraulic and three-electricity (particularly heavy-pressure system) control systems; 4) The section is smaller, and the realization of the heavy pressing of the convex roller is difficult.

In view of the above problems, the present invention proposes a method for rolling a square (or rectangular) slab, which is different from the conventional light rolling process in terms of controlling rolling position and rolling reduction, and is also different from the conventional heavy rolling method. The pressing method is very suitable for small square (or rectangular) billets, the requirements on equipment (particularly the distance between racks) are obviously lower than those of the traditional light pressing or current heavy pressing mode, and the defects of loose center, central shrinkage cavity, central carbon segregation and the like of the small square (or rectangular) billets of various steel types can be effectively controlled.

Disclosure of Invention

The invention provides a square (or rectangular) pressing method for solving the problems of the prior light pressing and heavy pressing technologies, and the specific technical scheme is as follows.

The continuous casting pressing method of the square (or rectangular) billet comprises the following steps: taking a transverse low-power sample from an unreeled casting blank, and obtaining a key rolling position from the transverse low-power sample by adopting a drilling and chip removing method; the first withdrawal and straightening machine after the critical position is pressed down by adopting a single-roller rule, and the withdrawal and straightening machine before the critical position is pressed down by adopting a multi-roller rule.

The drilling scrap taking method is that firstly, scrap iron samples are taken at the solidification center of a casting blank low-power sample by a drill bit with the diameter phi of 5mm, and then the scrap iron samples are taken along the vertical direction of the upper, lower, left and right in a cross shape to four directions respectively, the distance between sampling points is 15mm, and the number of the sampling points in each direction is more than or equal to 4.

The determination of the key position is to analyze the carbon content in the iron filings at each sampling point, and the arithmetic average value of the carbon content at each point and the carbon content at all points is used as the ratio, and the solid phase fraction of the center of the casting blank corresponding to the position with the ratio less than or equal to 0.95 is the key position from the solidification center point of the casting blank.

The single-roller rule means that single-roller pressing is adopted, and the pressing amount is more than or equal to 10mm.

The multi-roller rule is that the number of the adopted withdrawal and straightening machines is 2-3, the rolling reduction of the rolling rollers of each withdrawal and straightening machine is kept the same, and the total rolling reduction rate is controlled to be less than or equal to 3mm/m.

The applicable section is a square (or rectangular) blank with the thickness of 130mm-260 mm.

The invention has the following beneficial effects: 1) The invention provides a quantitative method for determining the control pressing parameters, which overcomes the defect of pressing at a manually specified multi-section or fixed position, and can rapidly determine the optimal pressing parameters of various steel types and sections; 2) The rolling method provided by the invention can overcome the phenomenon that shrinkage cavity and loose healing are insufficient in the traditional soft rolling, can also overcome the problem that the center segregation inhibition effect is not obvious in the traditional rolling technology, can effectively avoid the trouble of rolling cracks on the rolling technology, and can greatly improve the internal quality of casting blanks; 3) The rolling method provided by the invention solves the problems of small section, short solid-liquid two-phase area and difficult catching of rolling position of square (or rectangular) billet continuous casting machine, and has much smaller requirements on the distance between frames and a three-electric system than the traditional rolling method and the traditional rolling technology.

Drawings

FIG. 1 is a schematic diagram of scrap iron sampling points of a transverse low-power sample of an unreeled casting blank.

FIG. 2 is a schematic diagram of the solid phase fraction of the center of a casting blank corresponding to a position where the segregation ratio is less than or equal to 0.95.

FIG. 3 is a schematic diagram of the depressing method of the present invention.

FIG. 4 shows the determination of "key positions" under 200X 200 sections GCr 15.

FIG. 5 is a determination of the position of the 200X 200 section GCr15 push-down tension leveler.

FIG. 6 shows the longitudinal low-power result of 200X 200 sections under GCr15 pressure.

Detailed Description

The invention is further described below with reference to the drawings and examples.

Firstly, taking transverse low-power samples on a non-reduction casting blank, finding a solidification center, taking scrap iron samples by using a phi 5mm drill, respectively taking the scrap iron samples in four directions along the vertical direction of up, down, left and right in a cross shape, taking scrap iron intervals of 15mm, respectively taking more than or equal to 4 points in each direction, and FIG. 1 is a schematic diagram of scrap iron taking points of the non-reduction casting blank transverse low-power samples.

Secondly, the ratio of the carbon content of each point scrap iron to the arithmetic average value of all points is defined as segregation degree; taking the transverse distance of a casting blank as an X coordinate axis, taking the segregation degree as a Y coordinate axis, and taking an XY two-dimensional graph; meanwhile, using the transverse distance of the casting blank as an X coordinate axis, using the solid phase fraction of the center of the casting blank as a Y coordinate axis, and using the X and Y two-dimensional curve graph; the two graphs have a common X coordinate axis and can be manufactured into a double Y curve graph; in the figure, the center of the casting blank presents a positive segregation zone (namely, the segregation degree is larger than 1), negative segregation zones (namely, the segregation degree is smaller than 1) appear next to the two sides of the center point, and the solid phase fraction of the center of the casting blank corresponding to the position with the segregation degree ratio smaller than or equal to 0.95 is the key position from the center point of the casting blank outwards. FIG. 2 is a schematic diagram of the solid phase fraction of the center of a casting blank corresponding to a position where the segregation ratio is less than or equal to 0.95.

Thirdly, the first straightening and withdrawal machine behind the key position adopts single-roller regular pressing, and the pressing amount is more than or equal to 10mm; the multi-frame withdrawal and straightening machine in front of the key position adopts multi-roller regular rolling, the number of the adopted rolling frames is 2-3, the rolling reduction of each single roller is kept the same, and the total rolling reduction rate is controlled to be less than or equal to 3mm/m. FIG. 3 is a schematic diagram of the depressing method of the present invention.

The invention is described in detail below with reference to the drawings and examples.

Example 1.

A certain steel factory adopts a converter steelmaking-LF refining-VD vacuum-R12 m arc 200mm multiplied by 200mm continuous casting process to produce GCr15 billets. According to the weight percentage, the steel comprises the chemical components of C1.0 percent, (Si+Mn+Cr+Mo) =2.1 percent, and the balance of Fe and residual elements. In the continuous casting process, the pulling speed is 1.3m/min, the superheat degree of the tundish is controlled at 15-30 ℃, the secondary cooling specific water parameter is 0.24L/Kg, the electromagnetic stirring of the crystallizer is 400A/3Hz, and the electromagnetic stirring of the tail end is 550A/5.5Hz. The number of the casting and straightening machines is 6 (the numbers are 1# frame and 6# frame respectively), the upper rollers are driving rollers, and the roller spacing is 1.2m. The power of the 1# -4# power distribution machine is 5.5KW, the diameter of a hydraulic cylinder is 280mm, the diameter of a rod is 200mm, the stroke is 210mm, and the speed reduction ratio of a speed reducer is 647.3; the power of the 5# -6# distribution machine is 7.5KW. The diameter of the hydraulic cylinder is 320mm, the rod diameter is 220mm, the stroke is 210m, and the speed reducer has a speed reduction ratio 713.2. Taking a transverse sample of the non-rolling casting blank, respectively taking scrap iron samples along four directions along a solidification center in a cross shape according to a phi 5mm drill (the scrap taking distance is 15mm, and the points are respectively taken for 4 in each direction), and making a double Y curve graph (shown in figure 4) by using segregation degree data of each point and solid phase fraction of the center of the casting blank according to a model calculation result. In fig. 4, the "key position" is the position of the central solid phase fraction 0.7, and the corresponding distance from the meniscus is 13.5m (see fig. 5), measured as an index of the segregation ratio of 0.95 or less. The first drawing and straightening machine after 13.5m is subjected to single-roller regular pressing, and the pressing amount is 12mm; before 13.5m, the rolls were each pressed with 3 withdrawal devices to a single roll pressing amount of 2mm (pressing rate: 2.5 mm/m). FIG. 6 shows a longitudinal sample of the present depressing process, from which center porosity, center segregation lines, and V-type segregation lines were suppressed. And taking a scrap iron sample according to a casting blank solidification center, and obtaining the segregation degree of 1.06 through C/S analysis.

Example 2.

A certain steelworks adopts a converter steelmaking-LF refining-VD vacuum-R12 m arc 260mm x 280mm continuous casting process to produce GCr15 billets. According to the weight percentage, the steel comprises the chemical components of C1.0 percent, (Si+Mn+Cr+Mo) =2.1 percent, and the balance of Fe and residual elements. In the continuous casting process, the pulling speed is 0.75m/min, the superheat degree of the tundish is controlled at 15-30 ℃, the secondary cooling specific water parameter is 0.20L/Kg, the electromagnetic stirring of the crystallizer is 450A/3Hz, and the electromagnetic stirring of the tail end is 600A/5.5Hz. The number of the withdrawal and straightening machines is 7 frames (the numbers are 1# frame and 7# frame respectively), and the roller spacing is 1m. Taking a transverse low-power sample of the non-reduction casting blank, respectively taking scrap iron samples along four directions along a solidification center in a cross shape according to a phi 5mm drill (the scrap taking interval is 15mm, and the points are respectively taken for 4 in each direction), and making a double Y graph by using segregation degree data of each point and solid phase fraction of the center of the casting blank. The "critical position" is at a central solid fraction of 0.8 and is located between the 5# and 6# withdrawal and straightening machines from the meniscus position, measured as an index having a segregation ratio of less than or equal to 0.95. The single-roller regular pressing is implemented by using a No. 6 tension leveler, and the pressing amount is 14mm; the multi-roller regular rolling is implemented by 3 drawing and straightening machines 3# -5# in total, and the rolling reduction of each single roller is 2mm (the rolling reduction rate is 3 mm/m). And taking a scrap iron sample according to a casting blank solidification center, and obtaining the segregation degree of 1.08 by C/S analysis.

Example 3.

A certain steel factory adopts a converter steelmaking-LF refining-VD vacuum-R9 m arc 150mm multiplied by 150mm continuous casting process to produce No. 70 steel billet. According to the weight percentage, the steel comprises the chemical components of C0.7 percent, (Si+Mn+Cr+Mo) =0.8 percent, and the balance of Fe and residual elements. In the continuous casting process, the drawing speed is 1.45m/min, the superheat degree of the tundish is controlled at 15-30 ℃, the secondary cooling specific water parameter is 0.35L/Kg, the electromagnetic stirring of the crystallizer is 350A/3Hz, the electromagnetic stirring of the tail end is 400A/5.5Hz, the number of the casting and straightening machines is 4 frames (the numbers are 1# frame to 4# frame respectively), and the roller spacing is 1.35m. Taking a transverse sample of the non-reduction casting blank, respectively taking scrap iron samples along four directions along a solidification center in a cross shape according to a phi 5mm drill bit (the scrap taking distance is 15mm, and the points are respectively taken for 4 in each direction), and making a double Y graph by using segregation degree data of each point and solid phase fraction of the center of the casting blank. The "critical position" is obtained according to the method of this patent at a central solid fraction of 0.6, at a distance from the meniscus position between the 3# and 4# withdrawal and straightening machines. The single-roller regular pressing is implemented by using a No. 4 tension leveler, and the pressing amount is 10mm; the "multi-roll regular" rolling was carried out using a drawing machine # 2 and # 3, with each roll rolling reduction of 1mm (rolling reduction rate of 1.48 mm/m). And taking a scrap iron sample according to a casting blank solidification center, and obtaining the segregation degree of 1.09 through C/S analysis.

It should be understood that these examples are for the purpose of illustrating the invention only and are not intended to limit the scope of the invention. Furthermore, it is to be understood that various changes, modifications and/or variations may be made by those skilled in the art after reading the technical content of the present invention, and that all such equivalents are intended to fall within the scope of protection defined in the claims appended hereto.

Claims (6)

1. A method for pressing square (or rectangular) billet continuous casting is characterized in that: taking a transverse low-power sample from an unreeled casting blank, and obtaining a key rolling position from the transverse low-power sample by adopting a drilling and chip removing method; the first withdrawal and straightening machine after the critical position is pressed down by adopting a single-roller rule, and the withdrawal and straightening machine before the critical position is pressed down by adopting a multi-roller rule.

2. A method of reducing a square (or rectangular) billet in continuous casting according to claim 1, wherein: the drilling scrap taking method is to take scrap iron samples at the solidification center of a casting blank low-power sample by using a drill bit with the diameter phi of 5mm, and then take the scrap iron samples in four directions along the vertical direction in a cross shape, wherein the distance between sampling points is 15mm, and the number of the sampling points in each direction is more than or equal to 4.

3. A method of reducing a square (or rectangular) billet in continuous casting according to claim 1, wherein: the key position is the position of analyzing the carbon content in the iron filings at each sampling point, the arithmetic average value of the carbon content at each point and the carbon content at all points is used as the ratio, and the solid phase fraction of the casting blank center corresponding to the position with the ratio less than or equal to 0.95 is the key position from the casting blank solidification center point.

4. A method of reducing a square (or rectangular) billet in continuous casting according to claim 1, wherein: the single roller rule means that a single tension leveler is adopted for pressing, and the pressing amount is more than or equal to 10mm.

5. A method of reducing a square (or rectangular) billet in continuous casting according to claim 1, wherein: the multi-roller rule is that the number of the adopted withdrawal and straightening machines is 2-3, the rolling reduction of the rolling rollers of each withdrawal and straightening machine is kept the same, and the total rolling reduction rate is controlled to be less than or equal to 3mm/m.

6. A method of reducing a square (or rectangular) billet in continuous casting according to claim 1, wherein: a square (or rectangular) blank with a thickness of 130mm-260mm is suitable.